The present invention relates to a process for producing foam boards having improved sound insulation properties. In particular, the present invention relates to a process for aftertreating known foam boards by repeated compression.
Foam boards, for example made of polyolefin foams or made of polystyrene extruded or particle foam, have long been employed for thermal and sound insulation.
For sound insulation, in particular footfall sound insulation, preference is given to foam boards which have been elasticized by temporary compression in the direction of the board thickness.
For example, the use of elasticized EPS (expandable polystyrene) insulating boards for footfall sound insulation in accordance with DIN 18164 Part 2, Schaumkunststoffe als Dammstoffe fur das Bauwesen, is known. Boards of this type must have adequate resilience. The resilience is characterized in DIN 18 164 Part 2 in terms of the dynamic rigidity s' (also known as the impact sound reduction factor) of the insulating layer, including the air trapped in it.
For structural engineering reasons, footfall sound insulation boards must have a very low dynamic rigidity and a relatively highly restricted deformation under load (difference between the supplied or nominal thickness and the thickness under load, expressed as the (d.sub.L -d.sub.B) value of DIN 18164 Part 2).
This means that the degree of compression (also known as the degree of elasticization), and thus the deformation, of the foam structure can only be varied to a very limited extent.
In the known aftertreatment of foam boards by compression (also known as elasticization), foam boards typically having a density of from 8 to 10 kg/m.sup.3 are compressed once to a maximum extent of 66% of their original thickness, and this is maintained for a certain time (usually less than 60 seconds).
After the pressure is removed, a slight irreversible deformation of the cell structure remains, the cells having an anisotropy such that the ratio between the long and short axes is from 1.15 to 1.25. The dynamic rigidity values achieved, for example in a 25 mm thick foam board made of polystyrene particle foam, are around 10 MN/m.sup.3. The (d.sub.L -d.sub.B) values are from about 1 to 3 mm. Here it is frequently difficult to achieve dynamic rigidity values of not greater than 10 MN/m.sup.3 reproducibly.
It is an object of the present invention to improve the sound insulation properties of the known foam boards and in particular achieve simple and reliable control thereof.